AMD isn't making their chips cheaper than Intel across the board, you can make a good case for it for their Epyc or Threadripper SKUs being cheaper since it's 2~4x dies on the same package compared to the massive Intel monolithic dies, but even then I'd be cautious on making that statement because for one Intel is a lot more vertically integrated than AMD since they own their fabs and their 14nm node is very mature at this point. And for client & mobile it gets even trickier since AMD's dies range from being slightly larger to quite a lot larger than competing Intel ones in those segments.

It's not exactly a great metric, but Intel still has 64.5% gross margins compared to AMD's 40%, if there was a yield disparity you'd see Intel's margins dip, but they haven't really.